Maximal Square

Given a 2D binary matrix filled with 0's and 1's, find the largest square containing all 1's and return its area.

For example, given the following matrix:

Return 4.

 1 class Solution {
 2 public:
 3     int maximalSquare(vector<vector<char>>& matrix) {
 4         int n=matrix.size();
 5         if(n<1) return 0;
 6         int m=matrix[0].size();
 7         if(m<1) return 0;
 8         vector<vector<int>> size(n,vector<int>(m,0));
 9         int maxnum=0;
10         int i;
11         for(i=0;i<n;i++)
12         {
13             if(matrix[i][0]=='1')
14             {
15                 size[i][0]=1;
16                 maxnum=1;
17             }
18         }
19         for(i=0;i<m;i++)
20         {
21             if(matrix[0][i]=='1')
22             {
23                 size[0][i]=1;
24                 maxnum=1;
25             }
26         }
27         
28         int j;
29         for(i=1;i<n;i++)
30         {
31             for(j=1;j<m;j++)
32             {
33                 if(matrix[i][j]=='1')
34                 {
35                     size[i][j]=min(size[i-1][j-1],min(size[i-1][j],size[i][j-1]))+1;
36                     if(maxnum<size[i][j])
37                        maxnum=size[i][j];
38                 }
39                 else
40                     size[i][j]=0;
41             }
42         }
43         return maxnum*maxnum;
44     }
45 };